Cigarette smokers have more severe periodontal disease and more widespread colonization by periodontal pathogens than non-smokers. In addition, smokers respond less well to periodontal therapies, particularly mechanical therapies such as scaling and root planing (SRP) and surgery. Recent data from our laboratory have indicated that treatment that included antibiotics produced a better clinical effect in smokers than mechanical therapy alone. Thus, the purpose of the present investigation is to compare the immediate and long-term effects of 3 periodontal therapies on clinical, microbiological and host parameters in current and non-smokers. In this double blind, placebo-controlled, randomized study, 108 current smokers and 108 non smokers will be randomly assigned to 1 of 3 treatment groups: SRP alone; SRP + systemically administered metronidazole; SRP + systemically administered amoxicillin and metronidazole and local delivery of doxycycline at pockets greater than or equal to 4 mm. Plaque Index, Gingival Index, % of sites with bleeding on probing, suppuration, pocket depth and attachment level will be measured at 6 sites per tooth at all teeth excluding 3rd molars at baseline, 3, 6, 12, 18 and 24 months. Subgingival plaque samples taken from the mesial aspect of each tooth at the same time points will be analyzed individually for their content of 40 subgingival species using checkerboard DNA-DNA hybridization. Antibody levels to 20 subgingival species will be measured in serum samples taken at baseline, 6 and 24 months. Levels of IL-1 Beta, IL-10, and IFNgamma will be measured in GCF samples taken from the 4 deepest pockets at baseline, 3, 6 and 24 months. The major hypothesis to be tested is whether smokers respond better to periodontal therapies that include 1 or more antibiotics. Other hypotheses will test whether host and microbiological parameters differ between smokers and non-smokers and if such parameters are comparably altered after therapy in both groups. The results will be of immediate clinical benefit to the large segment of periodontal patients who smoke cigarettes. Smokers make up 26 - 30% of the adult population and form a disproportionately high segment of the population requiring periodontal treatment. They may have special needs in terms of periodontal therapy which should be clarified by the proposed investigation. In addition, the cigarette smoker is an example of a periodontal patient who is "compromised" in terms of his/her ability to cope with infectious diseases. The proposed investigation should provide a model to examine methods that could be useful in treating compromised patients whether compromised by harmful habits such as smoking, systemic disease, or genetic background.